1. Technical Field
This patent application relates generally to a fire fighting system that utilizes foam to suppress fires. More particularly, this patent application relates to a foam dispensing system that precisely mixes a foam concentrate with water to make fire fighting foam. This patent application also relates to methods of precisely mixing the foam concentrate with the water.
2. Related Art
In order to accurately assess the fire suppressing qualities of fire fighting foam, a known quantity of the foam must be applied to a test fire. Typically, this involves applying a precise mixture of water and foam concentrate to the test fire. Some known foam dispensing systems use devices such as venturis, bladders, and diaphragms to control the mixture of foam concentrate and water. However, these known foam dispensing systems often fail to provide adequate precision in the foam concentrate/water mixture, for example, when variations in pressure and/or flow rate occur. Other known foam dispensing systems use a variable speed pump to inject foam concentrate into the water. However, when the variable speed pump reaches the low end or the high end of its speed range (e.g., in response to changes in flow rate), the pump's accuracy decreases, thereby decreasing the precision of the foam concentrate/water mixture. The inaccuracies in the foam concentrate/water ratio of existing dispensing systems often render it difficult to precisely determine the quantity of foam being applied to the fire. This may not provide a significant problem when fighting real life fires, because any inaccuracy in the ratio of foam concentrate to water can be compensated for by applying more foam to the fire than is necessary to extinguish it (although this can result in wasted foam concentrate).
When the foam is being used in a testing environment, however, it is more important for the foam to comprise a precise mixture of foam concentrate and water. Known foam dispensing systems have often proved insufficient for use in testing environments, due to their inability to provide adequate precision in the foam concentrate/water ratio. Therefore, there remains a need in the art for foam dispensing systems and related methods that overcome the shortcomings of the prior art.